Conventional polycrystalline diamond, (“PCD”) may be formed by subjecting diamond particles in the presence of a suitable solvent metal catalyst material to processing conditions of high pressure/high temperature (HPHT), where the solvent metal catalyst promotes desired intercrystalline diamond-to-diamond bonding between the particles, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making such PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. FIG. 1 illustrates a microstructure of conventionally formed PCD material 10 including a plurality of diamond grains 12 that are bonded to one another to form an intercrystalline diamond matrix first phase. The catalyst/binder material 14, e.g., cobalt, used to facilitate the diamond-to-diamond bonding that develops during the sintering process is dispersed within the interstitial regions formed between the diamond matrix first phase. The term “particle” refers to the powder employed prior to sintering a superabrasive material, while the term “grain” refers to discernable superabrasive regions subsequent to sintering, as known and as determined in the art.
The catalyst/hinder material used to facilitate diamond-to-diamond bonding can be provided generally in two ways. The catalyst/binder can be provided in the form of a raw material powder that is pre-mixed with the diamond grains or grit prior to sintering. In some cases, the catalyst/binder can be provided by infiltration into the diamond material (during high temperature/high pressure processing) from an underlying substrate material that the final PCD material is to be bonded to. After the catalyst/binder material has facilitated the diamond-to-diamond bonding, the catalyst/binder material is generally distributed throughout the diamond matrix within interstitial regions thrilled between the bonded diamond grains. Particularly, as shown in FIG. 1, the binder material 14 is not continuous throughout the microstructure in the conventional PCD material 10. Rather, the microstructure of the conventional PCD material 10 may have a uniform distribution of binder among the PCD grains 12. The microstructure may include both diamond grain/hinder interfaces 15 and diamond grain/diamond grain interfaces 16.
Solvent catalyst materials may facilitate diamond intercrystalline bonding and bonding of PCD layers to each other and to an underlying substrate. Solvent catalyst materials used for forming conventional PCD may include metals from Group VIII of the Periodic table, such as cobalt, non or nickel and/or mixtures or alloys thereof, with cobalt being the most common. Conventional PCD may include from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. However, while higher metal content increases the toughness of the resulting PCD material, higher metal content also decreases the PCD material hardness, thus limiting the flexibility of being able to provide PCD tables having desired levels of both hardness and toughness. Additionally, when variables are selected to increase the hardness of the PCD material, brittleness also increases, thereby reducing the toughness of the PCD material.
Conventional PCD is stable at temperatures or up to 700-750° C. (1,292-1,382° F.), after which increases in temperature may result in permanent damage to and structural failure of PCD. For example, upon heating of PCD, the difference in the coefficient of thermal expansion of the binder material, which may be cobalt, as compared to diamond results in the cobalt and the diamond lattice expanding at different rates, which may cause cracks to form in the diamond lattice structure and result in deterioration of the PCD. High operating temperatures may also lead to back conversion of the diamond to graphite causing loss of microstructural integrity, strength loss, and rapid abrasive wear.
In order to overcome this problem, strong acids may be used to “leach” the cobalt from the diamond twice structure (either a thin volume or the entire body) to at least reduce the damage experienced from different expansion rates within a diamond-cobalt composite during heating and cooling. Briefly, a strong acid, such as nitric acid or combinations of several strong acids (such as nitric and hydrofluoric acid may be used to treat a PCD body, e.g., by submersing the body in the acid, thereby removing at least a portion of the catalyst from the PDC composite. By leaching out an amount of the catalyst, thermally stable polycrystalline (“TSP”) diamond may be formed in certain embodiments, a select portion of a diamond composite is treated, in order to gain thermal stability with less effect on impact resistance. As used herein, the term thermally stable polycrystalline (TSP) includes both of the above (i.e., partial and complete treatment). Interstitial volumes remaining after leaching may be reduced by either furthering consolidation or by reinfiltrating the volume with a secondary material.